1. Field of the Invention
The present invention relates to catalyst composition and a method of manufacturing the same and, more particularly, catalyst composition employing a perovskite composite oxide. Also, the present invention relates to a reforming catalyst for a fuel cell as an application of the catalyst composition, an electrode catalyst for a solid oxide electrolyte fuel cell, etc.
2. Description of the Related Art
In general, as the catalyst composition, there are employed many oxide supports such as various alumina, zirconia, etc. that are impregnated with the catalyst activating substance such as a noble metal, etc.
For example, as the methanol reforming catalyst employed as the fuel cell, a Cuxe2x80x94Zn based catalyst is known which contains the zirconia (ZrO2) support impregnated with Cu as the catalyst activating substance. The steam reforming reaction of the methanol is given by following Formula (1), and generates carbon dioxide (CO2) and hydrogen (H2) with the intervention of the reforming catalyst.
CH3OH+H2Oxe2x86x92CO2+3H2xe2x80x83xe2x80x83(1) 
Also, in Patent Application Publication H8-196907 published in 1996, a ruthenium catalyst that accelerates the steam reforming reaction by using the hydrocarbon gas such as butane, etc. is disclosed. This ruthenium catalyst is formed by impregnating zirconium (Zr), rare earth metals (Y, La), alkaline earth metals (Mg, Ca), and ruthenium (Ru) into various oxide supports such as alumina, silica, zirconia, etc., and then exhibits the high activity at the low steam/carbon ratio.
In the Cuxe2x80x94Zn reforming catalyst employed in the fuel cell, the steam reforming reaction given by Formula (1) as well as the methanol decomposition reaction given by following Formula (2) is accelerated to thus generate the carbon monoxide (CO).
CH3OHxe2x86x92CO+2H2xe2x80x83xe2x80x83(2) 
Since the generated CO serves as the degradation factor of the fuel cell, the high selectivity in reaction to suppress the CO generation low is required of the reforming catalyst.
However, in order to get the high selectivity in reaction by using the Cuxe2x80x94Zn based reforming catalyst while suppressing the CO generation, the catalyst must be employed in the relatively narrow temperature range (300xc2x0 C.xc2x120xc2x0 C.). If the catalyst temperature exceeds 320xc2x0 C., the methanol decomposition reaction proceeds abruptly to generate CO and cause the growth of the grain diameter of Cu. Thus, the performance of the catalyst itself is deactivated.
Also, the above ruthenium catalyst (Zrxe2x80x94(Y, La)xe2x80x94(Mg, Ca)xe2x80x94Ru) needs the high temperature of more than 650xc2x0 C., at which such catalyst exhibits the activity, and the high steam/carbon ratio of 3.0 to 1.85. Therefore, it is difficult to apply such catalyst to the fuel cell system equipped onto automobiles.
Meanwhile, recently there are many cases where the pre-thermal reforming reaction is employed to accelerate the steam reforming reaction given by Formula (1) as well as the partial oxidation reaction given by Formula (3) by adding the oxygen gas to the reforming reaction gas. Accordingly, the stability at the high temperature and oxidizing atmosphere is also required of the reforming catalyst.
CH3OH+xc2xdO2xe2x86x92CO2+2H2xe2x80x83xe2x80x83(3) 
It is a first object of the present invention to provide high activity/high selectivity catalyst composition capable of maintaining its high selectivity with the good stability even in the high temperature and oxygen sufficient atmosphere, and a method of manufacturing the same.
Also, it is a second object of the present invention to provide a reforming catalyst for a fuel cell, an electrode catalyst, a solid electrode type fuel cell, a reformer, and a fuel cell system, all using the above catalyst composition.
In order to achieve the above objects of the present invention, a catalyst composition of the present invention contains a perovskite composite oxide of the type expressed by a rational formula ABO3. Also, this rational formula ABO3 is expressed by a formula Axe2x80x21-xAxe2x80x3xBxe2x80x21-xcex1Bxe2x80x3yO3. Where the Axe2x80x3 is La and/or Ce, the Axe2x80x3 is at least one element selected from the group consisting of La, Ca, Sm, Ce, Sr, Ba and Pr, the Bxe2x80x2 is at least one element selected from the group consisting of Co, Fe, Mn and Gd, and the Bxe2x80x3 is at least one element of noble metals. In addition, preferably the noble metal in Bxe2x80x3 is at least one elements selected from the group consisting of Ru, Rh, Pd, and Pt.
The above catalyst composition of the present invention is the perovskite composite oxide expressed by the formula Axe2x80x21-xAxe2x80x3xBxe2x80x21-yBxe2x80x3yO3 and is material that is stable in the high temperature and oxidizing atmosphere. This catalyst composition has a function as the support and has an active catalytic function in itself since it contains the noble metal with an active catalytic function in the B site of the crystal structure. Thus, this catalyst composition can assure the high dispersibility and stability to thus exhibit the higher catalytic function than the case where the catalyst activating substance is simply impregnated. Also, this catalyst composition can exhibit the high electro-mobility based on the lattice defect in the A site and thus has a function as the electrode. These functions can be improved by selecting above optimal elements in respective sites.
Accordingly, the above catalyst composition of the present invention may be employed as the catalyst in various applications. In particular, this catalyst composition may be employed as the reforming catalyst to produce the hydrogen gas for the fuel cell. Also, since this catalyst composition has the catalytic function and the electro-mobility together, it can be employed as the electrode catalyst of the fuel cell.
In order to produce the catalyst composition of the present invention, first a mixed solution is prepared by mixing chloride, nitrate, or carbonate of La or Ce, at least one type of chloride, nitrate, and carbonate of at least one element selected from the group consisting of La, Ca, Sm, Ce, Sr, Ba, and Pr, at least one type of nitrate and carbonate of at least one element selected from the group consisting of Co, Fe, Mn, and Gd, and at least one type of chloride and nitrate of at least one element selected from the group consisting of Ru, Rh, Pd and Pt. Then, a monooxy carbonate is prepared as an intermediate product by reacting the mixed solution with a carbonate based on a hydrothermal reaction. Then, this monooxy carbonate is heated in an oxygen atmosphere.
A reforming catalyst of the present invention comprises a honeycomb substrate, and the above catalyst composition coated on the honeycomb substrate and set forth in the present invention.
An electrode catalyst for a fuel cell of the present invention comprises the above catalyst composition set forth in the present invention.
A solid oxide electrolyte fuel cell of the present invention comprises a solid electrolyte substrate, the electrode catalyst containing the catalyst composition set forth in the present invention adhered onto one surface of the solid electrolyte substrate and an air electrode adhered onto other surface of the solid electrolyte substrate.
A reformer of the present invention for reforming a fuel gas, comprises a gas inlet port, a reactor vessel in which the reforming catalyst containing the catalyst composition set forth in the present invention is provided to its inside and which causes a reforming reaction of a gas supplied from the gas inlet port, and a gas outlet port of a gas reformed by the reactor vessel.
Also, a reforming apparatus of the present invention, comprises a fuel gas supply source, an oxygen supply source, a steam supply source, a reformer set forth in the present invention, and pipings for supplying a fuel gas, an oxygen, and a steam supplied from respective supply sources to the reformer.
In addition, a fuel cell system of the present invention comprises a reforming apparatus set forth in the present invention, a fuel cell, pipings for supplying a gas reformed by the reforming apparatus to the fuel cell, and pipings for supplying a gas containing oxygen to the fuel cell.